The present invention is related to an improved roof assembly of the type utilizing flexible membrane material, preferably single-ply membrane material, as the uppermost part of the roof assembly. More specifically, the present invention is directed to an improved roofing assembly of this type, utilizing air permeable decking comprised of metal sheets, wood decking, concrete planking, and the like. Support metal decking sheets, having corrugations for reinforcement, have been previously used in roofing systems of the type using flexible single-ply membranes. These metal decking sheets are attached to an underlying roof support structure, such as metal I-beams, purlins, joists, a wood frame work, or the like. These metal decking sheets serve to support insulation boards on the top thereof, which insulation boards are then in turn covered by the single-ply membrane. Such metal roof decking sheets are commercially available from U.S. Steel and other suppliers. Air permeable wood decking and concrete planking decking are also readily commercially available through lumber and roofing supply outlets.
In order to accommodate the wind uplift forces that occur in use of such roofing assemblies on a building, especially the very high forces on tall buildings and adjacent perimeter edges of buildings, it has been known to provide venting valves at the membrane. See my U.S. Pat. Nos. 4,223,486 and 4,557,081 for an examples of venting valve systems that have been used. It has also been known to provide some type of sealing envelope that extends over the top of the sheet metal or other air permeable decking and effectively seals the insulation boards in an air-tight envelope when topped by the membrane, in certain areas of the perimeter and protrusions of the roof that is being covered.
In prior systems using single-ply membranes and a poured-in-place concrete deck, the deck serves as an air-tight seal. Flashing is provided between the concrete deck and the membrane overlying the insulation to form a sealed air-tight envelope at protrusions.
In all of the prior systems using some type of vapor barrier or seal placed upon the top of an air permeable decking, the wind uplift forces are transferred to the bottom of the vapor barrier sheet pushing upward from inside the building, and the integrity of the roof system vis-a-vis the wind uplift forces depends upon the integrity of the insulation and the fastener holding capability in the deck to maintain the insulation in place. Typically, the fasteners would penetrate the insulation boards and include an overlying washer-type hold-down member on top of the insulation. These fasteners would then be screwed or bolted to the air permeable decking underneath. Under certain wind uplift conditions, the connection between the insulation board fasteners and the decking can fail during wind uplift stress conditions resulting in the insulation board being pushed against the overlying membrane to cause a roof failure. Prior roofing systems did not employ air seal barriers from the interior of the building including at penetrations, and wind forces would then focus the stress of uplift pressures through the roof assembly directly into the water proofing membrane. These prior systems also required a barrier sheet to be interposed between the top of the decking and the bottom of the insulation board or board layers. This air barrier sheet would also then be penetrated by the fasteners for the hold-down of the insulation boards. Under certain circumstances during assembly of such roofs, the air barrier could tear at the location of the hold-down fasteners, thereby diluting the air barrier effect.
The above described disadvantages are avoided in a very simple manner according to the present invention. According to the present invention, the need for a vapor barrier between the decking and the insulation boards is obviated (i) by providing that the decking panels are sealed along all abutting or overlapping joints; (ii) by providing fasteners for holding the decking on the roof-support structure which are sealed against air leaks through the decking; and (iii) by sealing all perimeter and penetration sections. In especially preferred embodiments, equalizer valves are also provided in areas of concentrated wind lift vortice conditions to cause vacuum transfer into the roof system. Not only does this arrangement obviate the need for an air seal barrier between the insulation board and the air permeable decking, it also assures that the wind uplift stress forces are transferred through the top water proofing membrane and insulation to the decking, thereby relieving the insulation board and fasteners from forces that would otherwise act on them.
One advantageous consequence of the arrangement of the invention is that the insulation board fasteners need provide only minimal support to hold the board against warpage, requiring less fasteners and less sophistication of the fastening scheme for the insulation boards and membrane. It is a rather simple assembly matter to very rigidly fasten the air permeable panel decking to the underlying purlins, joists or the like, in view of the structural integrity of the decking and the purlins, joists or the like. Also, very reliable and repeatable hold-down fastening forces can be maintained between the sheet metal decking and the underlying roof-support purlins, joists, etc. to accommodate the projected wind uplift forces that might occur over particular areas of roof under various wind conditions.
According to certain preferred embodiments of the present invention, each of the fasteners which penetrate the decking are sealed at the penetrations. There are readily available commercial fastener screws and other fasteners which have self-sealing structures so that they form a good air-tight seal without any additional efforts on the part of the roof assembler. The overlapping or abutting joints of the decking sheets are sealed by roof flashing tape or by application of roof caulking according to different preferred embodiments of the invention. The lashing at the edge portions of the field of the roof being covered by the decking can be accomplished in much the same manner as would have been the case with the prior systems, except that additional flashing preferably seals to the edges of the decking. Consequently, this decking flashing connection at the perimeter and protrusion edge portion adds minimum expense and difficulty to the installation process.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.